Apparatus and Method for a Liquid Cooled Shield for Improved Piercing Performance

ABSTRACT

A shield for a plasma arc torch that pierces and cuts a metallic workpiece producing a splattering of molten metal directed at the torch, the shield protecting consumable components of the plasma arc torch from the splattering molten metal. The shield can include a body, a first surface of the body configured to be contact-cooled by a gas flow, a second surface of the body configured to be contact-cooled by a liquid flow, and a seal assembly configured to be secured to the body and disposed relative to the second surface configured to retain the liquid flow contact-cooling the second surface.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 12/046,670entitled “Liquid Cooled Shield for Improved Piercing Performance” filedon Mar. 12, 2008, the contents of which are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The invention generally relates to plasma arc torches. Morespecifically, the invention relates to a shield for protectingconsumables of a plasma arc torch.

BACKGROUND OF THE INVENTION

Basic components of modern plasma arc torches include a torch body, anelectrode (e.g., cathode) mounted within the body, a nozzle (e.g.,anode) with a central orifice that produces a pilot arc to the electrodeto initiate a plasma arc in a flow of a suitable gas (e.g., nitrogen oroxygen) and associated electrical connections and passages for cooling,and arc control fluids.

In piercing metal using a plasma arc torch, an important designconsideration is the ejection of molten metal from the cut kerf backonto the torch which can destroy the nozzle. There are two principalmodes for this destruction. First, molten metal ejected from the cutkerf can disturb the plasma jet causing it to gouge the nozzle. Second,the molten metal can solidify and adhere to the front face of thenozzle, which eventually causes an electrical bridging between thenozzle and the workpiece. This results in “double arcing” which candrastically reduce the life of a nozzle.

There have been several approaches to solving the gouging and doublearcing problems created by the ejection of molten metal. In high currentplasma cutting torches (e.g., 200 amperes and more), the solution hasbeen to use a multi-piece nozzle with water injection cooling. A typicalsuch nozzle of the type manufactured by Hypertherm, Inc. correspondingto Hypertherm Models HT400 and PAC500, the front face of the nozzle ismade of a ceramic. This arrangement controls gouging and double arcingbecause (1) the ceramic nozzle face is non-conducting and therefore willnot cause double arcing and (2) the nozzle is protected by the ceramicbarrier. Further the excellent cooling properties of the water,operating by cooling the ceramic nozzle piece and by water vapor coolingthe molten metal ejected during piercing, inhibit the molten metal frombonding or fusing to the ceramic element or in the extreme case, fromattacking the ceramic. A variation on the high-current, multi-componentnozzle similar to the nozzle sold by Hypertherm as its Model PAC500, isa ceramic nozzle piece incorporating is radial water injection, but theceramic nozzle piece is replaced by a copper front piece. An insulatingelement separates the nozzle components so that the front of the nozzleis floating electrically. The copper is more readily cooled than theceramic and it withstands abuse significantly better, and therefore hasa longer life.

In some cases, a ceramic insulating sleeve is attached to the outside ofthe nozzle in an attempt to protect the nozzle. This is a so-called“shield cup”. Its main purpose is to stop nozzle-to-workpiece contact.An operator can touch or drag the torch on the workpiece without doublearcing. This ceramic sleeve, however, offers no protection duringpiercing against molten metal splatter and the attendant gouging anddouble arcing problems. Also, the ceramic shield (1) is brittle andbreaks easily and (2) not having the protection of water cooling, isattacked by the molten metal ejected from the cut.

Cooling consumables (e.g., shield) of a plasma arc torch with a coolingliquid (e.g., water) can have safety benefits. Without liquid cooling,the consumables can reach extremely high temperatures that can pose asafety issue during use. A lossless cooling system allows the use of adry plasma and a dry cutting table. Dry tables can be desirable due tothe reduced mess and elimination of the need to dispose of theused/contaminated water, which can be considered to be hazardous waste.

SUMMARY OF THE INVENTION

The invention can overcome these problems using a gas and/or liquidcooled shield that operates at reduced temperatures and inhibits slagformation on an exposed surface of the shield during piercing, therebyextending the useful life of the shield and enhancing the cut quality ofa plasma arc torch. For example, formation/buildup of slag on the shieldcan affect defining an initial height of the torch, which can affect thecut quality of the plasma arc torch. Formation of slag on a shield canalso block vent holes and/or an orifice of the shield, affecting bothcut quality and the life of the shield (e.g., by affecting the abilityto cool the shield). Slag formation on a shield can, in some cases, canmelt the shield. By way of example, in some embodiments, if the plasmaarc torch is used to cut steel and the shield is made of copper, theslag can melt the shield, as steel has a higher melting point thancopper. Slag formation can also cause the shield to buildup heat to thepoint of the oxidation temperature of the shield (e.g., if the shield ismade from copper, heat buildup from the slag can cause high coppertemperatures that result in oxidation of the copper), thereby causingdegradation of the shield (e.g., at the edges of the orifice).

In one aspect, the invention features a shield for a plasma arc torchthat pierces and cuts a metallic workpiece producing a splattering ofmolten metal directed at the torch, the shield protecting consumablecomponents of the plasma arc torch from the splattering molten metal.The shield can include a body, a first surface of the body configured tobe contact-cooled by a gas flow and a second surface of the bodyconfigured to be contact-cooled by a liquid flow. The shield can alsoinclude a seal assembly configured to be secured to the body anddisposed relative to the second surface configured to retain the liquidflow contact-cooling the second surface.

In another aspect, the invention features a method for reducingformation of slag on a shield secured to a plasma arc torch that piercesand cuts a metallic workpiece producing splattered molten metal directedat the torch. The method can include the step of contact-cooling a firstsurface of the shield by a gas flow, contact-cooling a second surface ofthe shield by a liquid flow and providing a seal assembly to retain theliquid flow, the seal assembly configured to retain the liquid incontact with the second surface relative to a retainer cap of the plasmaarc torch. The method can also include conductively cooling a thirdsurface of the shield exposed to the splattered molten metal byproviding a thermal conductive path formed at least in part of athermally conductive material in thermal communication with the firstsurface and the second surface.

In yet another aspect, the invention features a method for reducingformation of slag on a shield secured to a plasma arc torch that piercesand cuts a metallic workpiece producing splattered molten metal directedat the torch. The method can include the step of rapidly cooling theshield secured to the plasma arc torch with a cooling medium flow,retaining the cooling medium flow in the plasma arc torch, andrepeatedly cooling the shield (e.g., cooling the shield a plurality oftimes, a plurality of cycles, etc.) to prevent formation of slag on asurface of the shield exposed to the splattered molten metal.

In one aspect, the invention features a shield for a plasma arc torchthat pierces and cuts a metallic workpiece producing a splattering ofmolten metal directed at the torch. The shield can include a portionconfigured to be directly cooled by a flowing liquid. The shield canalso include a first sealing mechanism and a second sealing mechanismdisposed relative to the portion directly cooled by a flowing liquid,the first and second sealing mechanism configured to retain the flowingliquid directly cooling the portion of the shield relative to a retainercap of the plasma arc torch.

In another aspect, the invention features a plasma arc torch system. Theplasma arc torch system can include a plasma arc torch, a cooling deviceconfigured to provide a cooling medium and a shield disposed relative tothe plasma arc torch, a first portion of the shield being exposed tosplattering molten metal. The shield can include a second portiondirectly cooled by the cooling medium flowing from the cooling device,the second portion in thermal communication with the first portionexposed to splattering molten metal. The shield can also include asealing device configured to retain the cooling medium flowing from thecooling device, the sealing device configured to retain the coolingmedium in contact with the second portion of the shield in the plasmaarc torch.

In yet another aspect, the invention features a retaining cap for aplasma arc torch that includes an outer component having an interiorsurface and an exterior surface which defines, at least in part, a firstliquid coolant channel. The retaining cap can include an inner componentcircumferentially disposed within the outer component and having anexterior surface and an interior surface which defines, at least inpart, a second liquid coolant channel. The retaining cap can alsoinclude a gas flow channel defined at least in part by the interiorsurface of the outer component and the exterior surface of the innercomponent. A port can be located at an end of the gas flow channelbetween the interior surface of the outer component and the exteriorsurface of the inner component.

In another aspect, the invention features a shield retaining cap forretaining a shield to a plasma arc torch. The shield retaining cap caninclude an outer component having an interior surface and an exteriorsurface and an inner component circumferentially disposed within theouter component and having an interior surface and exterior surface. Theshield retaining cap can also include a liquid coolant channel where afirst portion of the liquid coolant channel can be defined, at least inpart, by a portion of the interior surface of the inner component. Asecond portion of the liquid coolant channel can be defined, at least inpart, by the exterior surface of the inner component and the interiorsurface of the outer component. The shield retaining cap can include aport between the exterior surface of the inner component and theinterior surface of the outer component. The port can be disposed at anend of at least one of the outer component or the inner component of theshield retaining cap.

In another aspect, the invention features a retaining cap for a plasmaarc torch that includes a shell having an exterior surface that defines,at least in part, a first liquid coolant channel. A liner can becircumferentially disposed within the shell and have an interior surfacethat defines, at least in part, a second liquid coolant channel. Theretaining cap can also include a gas flow channel defined at least inpart by and located between the shell and the liner.

In another aspect, the invention features a shield retaining cap for aplasma arc torch that includes a shell, a liner disposedcircumferentially within an interior surface of the shell and a liquidcoolant channel. A first portion of the liquid coolant channel can bedefined, at least in part, by an interior surface of the liner. A secondportion of the liquid coolant channel can be defined, at least in part,by a portion of the interior surface of the shell. The second portion ofthe liquid coolant channel can also be defined, at least in part, by aportion of an exterior surface of the liner.

In another aspect, the invention features a method for cooling a plasmaarc torch. The method can include the step of directing a liquid coolantto an electrode, directing the liquid coolant to a nozzle through afirst liquid coolant channel defined, at least in part, by a firstretaining cap and directing the liquid coolant from the nozzle to ashield through a second liquid coolant channel defined, at least inpart, by a second retaining cap. Alternatively, the sequence in whichthe coolant is directed to the electrode, nozzle, and shield can bereversed or reordered.

In yet another aspect, the invention features a plasma arc torch systemthat includes a torch body including a plasma gas flow path fordirecting a plasma gas to a plasma chamber in which a plasma arc isformed, an electrode and a nozzle disposed relative to the electrode todefine the plasma chamber. The plasma arc torch system can also includea retaining cap as described above, secured relative to a nozzle. Theplasma arc torch system can also include a shield disposed relative tothe nozzle and a shield retaining cap as describe above, securedrelative to the shield.

In another aspect, the invention features a shield retaining cap for aplasma arc torch that includes a substantially cylindrical bodydimensioned to receive a shield of the plasma arc torch and a liquidcoolant channel defined by the substantially cylindrical body. Theliquid coolant channel can include a return path and a supply path whichdirects a coolant to impinge a circumferentially extending portion ofthe shield.

In other examples, any of the aspects above, or any apparatus or methoddescribed herein, can include one or more of the following features.

A seal assembly on a shield can be in mechanical communication with aretaining cap. In some embodiments, the shield is in communication withthe plasma arc torch, the shield generally surrounding a nozzle of theplasma arc torch.

In some embodiments, a shield can include a first surface of the bodyconfigured to be contact-cooled by a gas flow that convectively coolsthe first surface. The shield can include a second surface of the bodyconfigured to be contact-cooled by a liquid flow, where the liquid flowconvectively cools the second surface. The shield can include a regionconductively cooled by at least one of the gas flow or the liquid flow.In some embodiments, the region conductively cooled includes atemperature gradient across the region.

In some embodiments, the shield can also include a flange disposedproximally relative to a surface of the shield that is exposed to themolten metal, where at least a portion of the second surface of the bodyconfigured to be contact-cooled by a liquid flow, is disposed on theflange.

The shield can also include an orifice disposed at a distal end of abody of the shield. In some embodiments, the shield includes a thirdsurface disposed relative to a distal end of the body of the shield, thethird surface exposed to splattering molten metal. The second surfaceconfigured to be contact-cooled by a liquid flow, can be disposedproximally relative to the third surface. In some embodiments, the thirdsurface exposed to splattering molten metal is conductively cooled bythe liquid flow. The third surface exposed to splattering molten metalcan be conductively cooled by the gas flow.

In some embodiments, a second surface can be contact-cooled by a liquidflow, the second surface disposed relative to a first end of the shield.A shield can include a third surface exposed to splattered molten metal,and can be disposed relative to a second end of the shield. The shieldcan also include a flange disposed relative to the first end of theshield, at least a portion of the first surface (e.g., surfacecontact-cooled by a gas flow) and second surface disposed on the flange.In some embodiments, contact-cooling a second surface of a shield by theliquid flow includes providing for constant liquid flow around an outersurface of the shield.

Rapidly cooling a shield can include cooling the shield such that moltenmetal is cooled to prevent strengthening of the bond between the moltenmetal and the shield. In some embodiments, rapidly cooling a shieldincludes cooling the shield so that the shield stays at substantiallythe same temperature during piercing as before piercing by extractingthe heat from the molten metal in contact with the surface of theshield. In some embodiments, rapidly cooling a shield includescontact-cooling a surface of the shield in thermal communication withthe surface of the shield exposed to the splattered molten metal.

A surface of the shield exposed to the splattered molten metal can beconductively cooled. The shield can be cooled to below ambienttemperature. In some embodiments, the shield is cooled to below about 60degrees Fahrenheit.

The shield can also include a portion configured to be directly cooledby a gas. A shield can include a lip, wherein a portion of the shieldconfigured to be directly cooled by the liquid is disposed on the lip.In some embodiments, a portion of the shield configured to be directlycooled by a liquid is disposed on an outer surface of the shield. Thegas-cooled portion can be disposed on an inner surface of the shield.

The shield can include a sealing mechanism, which can include at leastone of an o-ring, epoxy seal or hard metal contact seal.

In some embodiments, a cooling device provides a cooling medium and thecooling device is a chiller. The cooling medium can repeatedly cool aportion of the shield. In some embodiments, the shield includes a firstportion exposed to splattering molten metal and a second portionrepeatedly cooled by a cooling medium (e.g., gas or liquid), the secondportion in thermal communication with the first portion exposed tosplattering molten metal.

A retaining cap can define a first liquid coolant channel and a secondliquid coolant. The first liquid coolant channel can be in fluidcommunication with the second liquid coolant channel. The first liquidcoolant channel can be a return flow of liquid coolant. The secondliquid coolant channel can be a supply flow of liquid coolant. In someembodiments, the retaining cap can include a gas flow channel thatsupplies a shield gas to a workpiece.

In some embodiments, an interior surface of an inner component of aretaining cap is secured relative to a nozzle of the plasma arc torch.The interior surface of the inner component of a retaining cap caninclude a sealing assembly that seals liquid coolant relative to aplasma arc torch body. The interior surface of the inner component and aplasma arc torch body define, at least in part, the second liquidcoolant channel. In some embodiments, a retaining cap includes an outercomponent where the exterior surface of the outer component and an outerretaining cap of the plasma arc torch define, at least in part, thefirst liquid coolant channel.

A shield retaining cap can have an inner and outer component, where atleast one of the inner component or the outer component is securedrelative to a shield. In some embodiments, a shield retaining capincludes a port that is disposed at an end of the liquid coolant channeldefined by or formed by the shield. The liquid coolant channel candirect a coolant on to a shield. In some embodiments, a first portion ofthe liquid coolant channel is a coolant supply flow and a second portionof the liquid coolant channel is a coolant return flow. In someembodiments, an interior surface of the inner component of the shieldretaining cap and an inner retaining cap define at least in part, thefirst portion of the liquid coolant channel.

In some embodiments, a temperature of the coolant impinging the shieldis consistent at each point along the circumferentially extendingportion of the shield. The shield retaining cap can define, at least inpart, a liquid coolant channel that directs a coolant to a portion ofthe shield. In some embodiments, a shield retaining cap has asubstantially cylindrical body that includes a substantially cylindricalouter component and a substantially cylindrical inner component disposedwithin the outer component. A supply path for a liquid coolant channelcan be formed at least in part by an interior surface of thesubstantially cylindrical inner component. A return path of a liquidcoolant channel can be formed at least in part by an exterior surface ofthe substantially cylindrical inner component and an interior surface ofthe substantially cylindrical outer component.

Other aspects and advantages of the invention can become apparent fromthe following drawings and description, all of which illustrate theprinciples of the invention, by way of example only.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the invention described above, together with furtheradvantages, may be better understood by referring to the followingdescription taken in conjunction with the accompanying drawings. Thedrawings are not necessarily to scale, emphasis instead generally beingplaced upon illustrating the principles of the invention.

FIG. 1 is a drawing of a shield according to an illustrative embodiment.

FIG. 2 is a cross section of a shield according to an illustrativeembodiment.

FIG. 3 is a partial cross section of the shield and a plasma arc torchaccording to an illustrative embodiment.

FIG. 4 is another cross sectional view of the shield and plasma arctorch according to an alternative illustrative embodiment.

FIG. 5 is drawing depicting a shield cooled by a liquid, according to anillustrative embodiment.

FIG. 6 is a graph demonstrating slag accumulation in pierce protocoltests utilizing a shield according to an illustrative embodiment.

FIG. 7 is a graph demonstrating slag on a chilled versus a cooled shieldin pierce protocol tests utilizing a shield according to an illustrativeembodiment.

FIG. 8 is a partial cross sectional drawing of a stackup of consumablesfor a plasma arc torch according to an illustrative embodiment.

FIG. 9 is a cutaway drawing of consumables for a plasma arc torchaccording to an illustrative embodiment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a drawing of a shield 5 according to an illustrativeembodiment. The shield 5 can be disposed relative to a plasma arc torchthat pierces and cuts a metallic workpiece producing a splattering ofmolten metal directed at the torch. The shield 5 can protect consumablecomponents of the plasma arc torch from the splattering molten metal.The shield includes a body. In this embodiment, the body of the shieldincludes a first surface that is configured to be contact-cooled by agas flow (not shown). Contact-cooling can include cooling a portion ofthe shield (e.g., surface) by contacting it with a coolant (e.g.,cooling medium, cooling liquid, cooling gas, etc.). In some embodiments,the surface cooled by the gas flow is an internal surface (e.g., hole,exit port) disposed relative to the shield. The body of the shield alsoincludes a second surface 10 configured to be contact-cooled by a liquidflow. In some embodiments, the body of the shield includes two pieces.In some embodiments, cooling the shield 5 involves providing forconstant liquid flow around an outer surface of the shield 5. In thisembodiment, the shield 5 also includes a seal assembly 15A and 15B(e.g., o-ring, epoxy seal, hard metal contact on high tolerancesurfaces, or any combination thereof) configured to be secured to thebody (e.g., an o-ring disposed on the shield 5 in a channel disposedrelative to the shield 5, an o-ring disposed on the shield 5 without achannel disposed relative to the shield, feature of the body sealing theliquid flow relative to a retainer cap, or any combination thereof), theseal assembly 15A and 15B disposed relative to (e.g., adjacent to) thesecond surface 10. The seal assembly 15A or 15B can be configured toretain the liquid flow contact-cooling the second surface 10.

In some embodiments, the shield 5 is comprised of a material thatprovides for a consistent thermal medium (e.g., metal) so that a surface20 of the shield exposed to a splattering molten metal is conductivelycooled as a result of at least one of the liquid flow contact-coolingthe second surface 10 or the gas flow contact-cooling the first surface(not shown). In some embodiments, conductively cooling a portion (e.g.,surface, region) of the shield includes cooling within a portion of theshield having a temperature gradient across that portion of the shield.The shield 5 also can include exit ports 25 for a shielding gas to exit,providing protection to the shield 5. The shield 5 also includes an exitorifice 30 that permits the passage of a plasma arc and a flow of a gas.

Keeping a shield 5 cool can increase the pierce thickness capability andalso prevent the formation of a good bond between the molten slag andthe shield 5. In some embodiments, cooling the shield 5 includeschilling the shield 5. In some embodiments, the liquid flow has a lowenough temperature (e.g., less than about 60 degrees Fahrenheit or 40degrees Fahrenheit) that the liquid flow chills the shield 5 bycontact-cooling the second surface 10 and conductively chilling the restof the shield 5. Reduced slag accumulation on the shield 5 extends thelife of the shield 5. Reducing slag accumulation on the shield 5 reducesthe chances of molten metal disturbing the plasma jet and gouging thenozzle and/or double arcing between the nozzle and the workpiece.Reduced shield temperature extends the thickness capability. Piercing ofthick metal has been limited due to the relatively long pierce timesneeded to allow the arc to melt though the metal and because of theresultant molten slag which is blown back at the torch (e.g., primarilythe shield 5). For example, the HT4400 400A process is limited topiercing 1¼″ mild steel (MS). In some embodiments, when trying to piercethicker steel, the shield 5 will eventually melt because the onlycooling of the shield 5 is through the shield gas. Often when piercingsteel of 1″ and greater, the slag begins to accumulate on the shield 5and if not cleaned off, the shield performance will begin to deteriorateas slag build up continues. Eventually the cut quality will beunacceptable or the shield 5 may even melt due to the large mass of hotsteel. In some tests, it was discovered that the shield 5 accumulatedlarge amounts of slag within 25 pierces. With accumulated slag, theshield 5 can melt and render the torch incapable of further pierces. Insome embodiments, the piercing protocol requires that the process beable to pierce a given thickness of plate 300 times without operatorintervention (e.g., cleaning the slag off the shield 5 between pierces).

FIG. 2 is a drawing of a cross section of a shield 5 according to anillustrative embodiment. In this embodiment, the shield 5 is disposedrelative to a nozzle (not shown). In some embodiments, the shield 5includes hole features 32 (e.g., exit ports) for a gas to flow throughthe hole features and through the exit ports of the shield 25. In someembodiments, the shield 5 includes a first surface 35, a second surface10 and a third surface 20. The third surface 20 can be conductivelycooled by at least one of liquid flow or gas flow. In some embodiments,second surface 10 is contact-cooled (e.g., cooling the surface bycontacting it with a cooling medium) using a liquid to thereby produceconductive cooling and achieve a low temperature on the third surface20, which can be exposed to molten metal during operation of a torch. Insome embodiments, third surface 20 is conductively cooled as a result ofcontact-cooling the first surface 35 with a gas flow and/orcontact-cooling the second surface 10 with a liquid flow.

In some embodiments, the second surface 10 is disposed relative to afirst end 36 (e.g., proximal end) of the shield 5. In some embodiments,the shield 5 includes a body including an orifice disposed at a secondend (e.g., distal end) of the body of the shield. The shield 5 caninclude a third surface 20 that is exposed to the splattering moltenmetal and is not contact-cooled by the liquid flow or the gas flow. Thethird surface 20 can be conductively cooled by the gas flowcontact-cooling the first surface 35 or the liquid flow contact-coolingthe second surface 10. In some embodiments, the third surface 20 isdisposed on an outer surface of the shield and the second surface 10 isdisposed proximally relative to the third surface 20. In someembodiments, the third surface 20 exposed to molten metal is disposedrelative to the second end 37 (e.g., distal end) of the body of theshield. In some embodiments, the second surface 10, which iscontact-cooled by the liquid flow, is disposed proximally relative tothe third surface 20 exposed to the molten metal. The shield 5 can alsoinclude a flange 40 disposed relative to the first end 36 of the shield5, at least a portion of the first surface 35 and/or second surface 10disposed on the flange 40. In some embodiments, the third surface 20 canbe disposed distally relative to the flange 40. The flange 40 can bedisposed proximally relative to the third surface 20 (e.g., the surfaceof the shield exposed to the molten metal). In some embodiments, atleast a portion of the first surface 35, which is contact-cooled by agas flow, is disposed on an inner surface of the flange 40 or the shield5. In some embodiments, at least a portion of the second surface 10,which is contact-cooled by a liquid flow, is disposed on an outersurface of the flange 40 or the shield 5.

In this embodiment, the first surface 35 contact-cooled by a gas flow isdisposed on an inner surface of the shield that is not exposed tosplattering molten metal. In some embodiments, the gas flow convectivelycools the first surface 35. In this embodiment, the second surface 1 0contact-cooled by the liquid flow is disposed on an outer surface of theshield. In some embodiments, cooling the shield 5 involves providing forconstant liquid flow around an outer surface of the shield 5. In someembodiments, the liquid flow convectively cools the second surface 10.In some embodiments, the shield 5 includes a flange 40 (e.g., lip) andat least a portion of the first surface 35 and at least a portion of thesecond surface 10 are disposed relative to the flange 40.

The shield 5 can include a region 45 that is conductively cooled (e.g.,cooling occurring within the region with a temperature gradient acrossthe region) by at least one of the gas flow or the liquid flow. Theregion 45 can be any part of the shield that is not in contact with thecoolant (e.g., cooling medium such as a liquid or gas). In someembodiments, the region is the surface of the shield exposed tosplattered molten metal or even a part of the shield below the surfacein contact with the coolant. In some embodiments, the liquid flow has alow enough temperature (e.g., less than about 60 degrees Fahrenheit or40 degrees Fahrenheit) that the liquid flow chills the shield 5 bycontact-cooling the second surface 10 and conductively chilling the restof the shield 5. The shield 5 is configured so as to provide a thermallyconductive path between at least the first surface 35 or second surface10 to the conductively cooled region 45. In some embodiments, the shield5 is a unitary structure made of metal or a thermally conductive medium.In some embodiments, the shield 5 is comprised of a plurality ofstructures comprised of a consistent thermal medium, forming aconsistent thermally conductive path. In some embodiments, the shield 5is comprised of a plurality of structures having similar thermalproperties.

The shield 5 can be for a plasma arc torch (not shown) that pierces andcuts a metallic workpiece producing a splattering of molten metaldirected at the torch. The shield 5 can include a portion configured tobe directly cooled by a flowing liquid (e.g., the second surface 10) anda first sealing mechanism 15A and a second sealing mechanism 15Bdisposed relative to the portion cooled by the liquid. The portionconfigured to be directly cooled by the liquid (e.g., the second surface10) can be disposed on an outer surface of the shield 5 and the portionconfigured to be directly cooled by the gas can be disposed on an innersurface of the shield 5. The first and second sealing mechanism 15A and15B can be configured to retain the flowing liquid directly cooling theliquid-cooled portion of the shield (e.g., the second surface 10)relative to a retainer cap (not shown) of a plasma arc torch. Thesealing mechanism 15A or 15B can be at least one of an o-ring, epoxyseal or hard metal contact seal. The shield can also include a portionconfigured to be directly cooled by a gas (e.g., first surface 35). Theshield can also include a lip (e.g., flange 40), wherein the portionconfigured to be directly cooled by the liquid (e.g., the second surface10) is disposed on the lip (e.g., flange 40).

In some embodiments, a method for reducing formation of slag on a shield5 secured to a plasma arc torch (not shown), that pierces and cuts ametallic workpiece producing splattered molten metal directed at thetorch, can include contact-cooling a first surface 35 of the shield 5 bya gas flow. The method can also include contact-cooling a second surface10 of the shield 5 by a liquid flow and providing a seal assembly 15Aand 15B to retain the liquid flow, the seal assembly 15A and 15Bconfigured to retain the liquid in contact with the second surface 10relative to a retainer cap (not shown) of the plasma arc torch. Themethod can also include conductively cooling a third surface 20 of theshield 5 exposed to the splattered molten metal by providing a thermalconductive path formed at least in part of a thermally conductivematerial in thermal communication with the first surface 35 and thesecond surface 10. The step of contact-cooling the second surface 10 bythe liquid flow can include providing for constant liquid flow around anouter surface of the shield 5.

FIG. 3 is a partial cross section of a shield 50 disposed relative to aplasma arc torch 55, according to an illustrative embodiment. The shield50 can be in communication with a plasma arc torch 55. In someembodiments, the shield 50 includes a seal assembly 60A and 60B inmechanical communication with a retainer cap 65 of the plasma arc torch55. In some embodiments, the seal assembly 60A and 60B of the shield 50is a plurality of o-rings. The o-rings can be configured to retain theliquid flow contact-cooling the second surface 70 of the shield (e.g.,cooling a surface by contacting it with a coolant). In some embodiments,cooling the shield 50 involves providing for constant liquid flow aroundan outer surface of the shield 50. In some embodiments, the liquid flowhas a low enough temperature (e.g., less than about 60 degreesFahrenheit or 40 degrees Fahrenheit) that the liquid flow chills theshield 50 by contact-cooling the second surface 70 and conductivelychilling the rest of the shield 50 (e.g., chilling occurring within therest of the shield with a temperature gradient across the rest of theshield 50). In this embodiment, the shield 50 is secured to the plasmaarc torch 55 so that the shield 50 is in mechanical communication withthe retaining cap 65, forming a path 75 that allows for a liquid to flowfrom a source (not shown) through the plasma arc torch 55, flow to andcontact-cool the second surface 70 of the shield 50 and flow backthrough the plasma arc torch 55.

A method for reducing formation of slag on a shield 50 secured to aplasma arc torch 55, that pierces and cuts a metallic workpieceproducing splattered molten metal directed at the torch 55, can includerapidly cooling the shield 50 secured to the plasma arc torch 50 with acooling medium flow. The method can include retaining the cooling mediumflow in the plasma arc torch 55 and repeatedly cooling the shield 50(e.g., cooling the shield a plurality of times, a plurality of cycles,etc.) to prevent formation of slag on a surface of the shield exposed tothe splattered molten metal. The step of rapidly cooling can includecooling the shield 50 such that molten metal is cooled to preventstrengthening of the bond between the molten metal and the shield 50.Rapidly cooling the shield 50 can also include cooling the shield 50 sothat the shield 50 stays at substantially the same temperature duringpiercing as before piercing by extracting the heat from the molten metalin contact with the surface of the shield 50. The step of rapidlycooling the shield 50 can include contact-cooling a surface of theshield 50 in thermal communication with the surface of the shield 50exposed to the splattered molten metal. The surface of the shield 50exposed to the splattered molten metal can be conductively cooled. Insome embodiments, the shield 50 is cooled to below ambient temperature.The shield can be cooled to below about 60 degrees Fahrenheit.

FIG. 4 is another cross sectional view of the shield 50 and plasma arctorch according to an illustrative embodiment. The plasma arc torch 55includes a torch body 80, an electrode 85 (e.g., cathode) mounted withinthe body, a nozzle 90 (e.g., anode) with a central orifice 95 thatproduces a pilot arc to the electrode 85 to initiate a plasma arc. Alsodepicted are associated electrical connections and passages for plasmagas 100A, passages for cooling liquid 100B, and passages for shield gas100C. In this embodiment, the shield 50 is disposed relative to a plasmaarc torch 55. The shield 50 generally surrounds the nozzle 90. In someembodiments, the shield 50 includes a flange 105. The shield 50 alsoincludes a securing device 110 to secure the shield 50 to the plasma arctorch 55. The securing device 110 can be a threaded portion that can bescrewed on to the torch body 80 or on a retainer cap 65. In thisembodiment, a path 75 allows for a liquid to flow from a source (notshown) through the plasma arc torch 55, cool the electrode 85, cool theouter surface of the nozzle 90, flow to and contact-cool the secondsurface 70 of the shield 50 and flow back through the plasma arc torch55. In some embodiments, components of the plasma arc torch 55 (e.g.,electrode 85, nozzle 90, shield 50) can be cooled in adifferent/alternative sequence. In some embodiments, cooling the shield50 involves providing for a constant liquid flow around an outer surfaceof the shield 50.

In some embodiments, the first surface 115 contact-cooled (e.g., coolingby contacting a surface with a coolant) by a gas flow is disposed on aninner surface of the shield 50. The shield 50 can include passages forthe gas flow to exit, allowing the gas flow to not only contact-cool thefirst surface 15, but also act as a shielding gas that protects theshield 50 from the splattering molten metal as it exits the shield. Insome embodiments, the shield 50 includes a flange 105 and at least aportion of the first surface 115 is disposed on an inner surface of theflange 105.

In some embodiments, the shield 50 includes a flange 105 and at least aportion of the second surface 70 contact-cooled by a liquid flow isdisposed on an outer surface of the flange 105. In some embodiments, theliquid flow contact-cools the second surface 70 of the shield 50 byproviding for constant liquid flow around the outer surface of theshield 50. In some embodiments, constant liquid flow is provided aroundan outer surface of the flange 105.

In some embodiments, the liquid flow has a low enough temperature (e.g.,less than about 60 degrees Fahrenheit or 40 degrees Fahrenheit) that theliquid flow chills the shield 50 by contact-cooling the second surface70 and conductively chilling the rest of the shield 50 (e.g., chillingoccurring within the rest of the shield with a temperature gradientacross the rest of the shield 50). As can be seen in FIG. 4, the shieldcan include a third surface 125 that is disposed on an outer surface ofthe shield and is exposed to the splattering of molten metal when theplasma arc torch pierces and cuts a metallic workpiece. The shield 50 iscomprised of a consistent thermal medium, allowing the third surface 125to be conductively cooled by at least one of the gas flow or the liquidflow.

In some embodiments, a plasma arc torch system can include a plasma arctorch 55, a cooling device (not shown) configured to provide a coolingmedium and a shield 50 disposed relative to the plasma arc torch 55, afirst portion of the shield being exposed to splattering molten metal(e.g., third surface 125). The shield 50 can include a second portiondirectly cooled by the cooling medium (e.g., first surface 115, secondsurface 70 or any combination thereof) flowing from the cooling device,the second portion (e.g., first surface 115, second surface 70 or anycombination thereof) in thermal communication with the first portionexposed to splattering molten metal. A sealing device (e.g., sealassembly 60A or 60B) can also be configured to retain the cooling mediumflowing from the cooling device, the sealing device configured to retainthe cooling medium in contact with the second portion of the shield inthe plasma arc torch. The cooling device can be a chiller. In someembodiments, the cooling medium repeatedly cools (e.g., cooling theshield a plurality of times, a plurality of cycles, etc.) the secondportion.

FIG. 5 is drawing depicting a shield 130 cooled by a liquid, accordingto an illustrative embodiment. In this embodiment, the liquid flows fromthe supply 135 through a supply channel 140, through an annular coolingplenum 145, the liquid flow contact-cooling (e.g., cooling a portion orsurface by contacting it with a coolant or cooling medium) a portion ofan outer surface 155 on the shield. In some embodiments, the shield 130comprises a flange 150 and the liquid flow contact-cools a portion of anouter surface of the shield 155 on the flange 150. In this embodiment,after contact-cooling a portion of an outer surface of the shield 155,the liquid flows from the shield 130 through a return channel 160. Thisembodiment can allow for a constant liquid flow around an outer surfaceof the shield 130.

In some embodiments, the outer surface 155 of the shield, which iscontact-cooled by the liquid flow, is disposed relative to a first end161 of the shield 130. In some embodiments, the shield includes asurface exposed to splattering molten metal 165 disposed relative to asecond end 162 (e.g., distal end) of the shield 130. In someembodiments, the outer surface 155, which is contact-cooled by theliquid flow, is disposed proximally relative to the surface exposed tothe splattering molten metal 165.

Retaining the liquid flow permits lossless contact-cooling of the shield130 by the liquid flow. The shield 130 is comprised of a material thatprovides a consistent thermal medium (e.g., metal). Providing for aconstant liquid flow contact-cooling a portion of an outer surface ofthe shield conductively (e.g., cooling occurring in a portion of anouter surface of the shield with a temperature gradient across theportion of an outer surface of the shield), and repeatedly (e.g.,cooling the shield a plurality of times, a plurality of cycles, etc.),cools the surface exposed to splattering molten metal 165. Providing forthe constant liquid flow permits rapid and repeated cooling of theshield 130 (e.g., by conductive cooling) to prevent formation of slag ona surface of the shield exposed to the splattered molten metal 165. Insome embodiments, the liquid flow has a low enough temperature (e.g.,less than about 60 degrees Fahrenheit or 40 degrees Fahrenheit) that theliquid flow chills the shield 130 by contact-cooling a portion of anouter surface of the shield 155 and conductively chilling the rest ofthe shield 130.

Rapidly cooling a shield prevents bonding between molten metal with theshield and/or prevents strengthening of the bond between the moltenmetal and shield. For example, rapidly cooling the shield can includecooling the shield fast enough to repeatedly cool (e.g., cooling theshield a plurality of times, a plurality of cycles, etc.) molten sprayto: i) prevent bonding of molten metal to the shield or ii) preventmolten metal from coming into strong contact with the shield prior tosolidification of the molten metal. Rapidly cooling the shield caninclude contact-cooling at least a portion of a surface of the shield orconductively cooling regions of the shield. Rapidly cooling the shieldcan include cooling the shield so that the shield remains atsubstantially the same temperature during a spray of molten metal byextracting the heat from the molten metal in contact with the shield.Rapid cooling of the shield can be achieved through the embodimentsdescribed in FIGS. 1-5.

FIG. 6 is a graph 170 demonstrating slag accumulation in pierce protocoltests utilizing a shield according to an illustrative embodiment. Pierceprotocol tests were conducted with the shield/outer cap assembly beingweighed after every 25 pierces as an indicator of the slag accumulationlevel. The tests were done using 1½″ mild steel (MS). The x-axis 175 ofthe graph indicates the number of pierces and the y-axis 180 of thegraph indicates the slag mass that was accumulated. Three differentlevels of bulk coolant temperature were used: 135 degrees Fahrenheit, 85degrees Fahrenheit, and 38 degrees Fahrenheit. The cooling fluid waswater and the 38 degrees Fahrenheit was chosen as the lower end of thewater's usable temperature. The performance can be enhanced if additiveswere used, or even other liquids (e.g., glycol). The protocol testresults indicated that cooling the shield allowed the shield to lastthroughout the 300 pierces. The graph 170 shows that the when the shieldwas not cooled, the shield melted before 50 pierces could be achieved.The 38 degrees Fahrenheit water temperature resulted in a reduced amountof slag accumulating on the shield.

FIG. 7 is an alternative graph 185 depicting the data from FIG. 6demonstrating slag on a chilled versus a cooled shield in pierceprotocol tests utilizing a shield according to an illustrativeembodiment. In FIG. 7, the x-axis 190 indicates the three differentlevels of bulk coolant temperature used in the pierce protocol test: 135degrees Fahrenheit, 85 degrees Fahrenheit, and 38 degrees Fahrenheit.The y-axis 195 indicates the sum of the measured slag through 300pierces utilizing the shield according to an illustrative embodiment.The graph 185 demonstrates that a lower temperature of the cooled shieldcorrelates to a lower sum of measured slag through the 300 pierces. Forexample, a shield cooled at 135 degrees Fahrenheit accumulated a sum of198 grams of slag through the 300 pierces during the pierce protocoltests. A shield cooled at 85 degrees Fahrenheit accumulated a sum of 175grams of slag through the 300 pierces during the pierce protocol tests.In comparison, a shield chilled at 38 degrees Fahrenheit accumulated asum of 31 grams of slag through the 300 pierces during the pierceprotocol tests.

FIG. 8 is a partial cross sectional drawing of a stackup of consumablesfor a plasma arc torch 200 according to an illustrative embodiment. Theplasma arch torch 200 can include an electrode (e.g., electrode 85 ofFIG. 4) shield 205, nozzle 210, a retaining cap 215 that can be securedrelative to the nozzle 210 and a shield retaining cap 220 that can besecured relative to the shield 205. The plasma arc torch can includeliquid coolant channels 225A, 225B, and 230. The plasma arc torch canalso have a gas flow channel 235.

The plasma arc torch 200 can include a torch body (e.g., torch body 80of FIG. 4) including a plasma gas flow path for directing a plasma gasto a plasma chamber in which a plasma arc is formed. The plasma chambercan be defined at least in part by the electrode and a nozzle 210disposed relative to the electrode to define the plasma chamber. Aninner retaining cap (e.g., retaining cap 215) can be secured relative tothe nozzle 210. In some embodiments, a shield 205 is disposed relativeto the nozzle 210 and an outer retaining cap (e.g., shield retaining cap220) is secured relative to the shield 205.

Retaining cap 215 (e.g., nozzle retaining cap) can include an outercomponent 240 and inner component 245. The outer component 240 can havean interior surface 250 and an exterior surface 255. The exteriorsurface 255 of the outer component can define, at least in part, aliquid coolant channel 225A. The retaining cap 215 can also include aninner component 245 circumferentially disposed within the outercomponent 240. The inner component 245 can have an exterior surface 260and an interior surface 265. The interior surface 265 of the innercomponent 245 can be secured relative to a nozzle 210 of the plasma arctorch 200.

The gas flow channel 235 of the plasma arc torch 200 can be defined atleast in part by the interior surface 250 of the outer component 240 andthe exterior surface 260 of the inner component 245 of the retaining cap215. A port 270 (e.g., exit port) can be disposed at an end of the gasflow channel 235. The port 270 can be disposed between the interiorsurface 250 of the outer component 240 and the exterior surface 260 ofthe inner component 245 of the retaining cap 215.

The interior surface 265 of the inner component 245 can define, at leastin part, another liquid coolant channel 230. In some embodiments, theinterior surface 265 of the inner component 245 can include sealingassembly 275 that seals liquid coolant relative to a plasma arc torchbody. The interior surface 265 of the inner component 245 and the plasmaarc torch body can define, at least in part, liquid coolant channel 230.The exterior surface 255 of the outer component 240 and a shieldretaining cap 220 (e.g., outer retaining cap) of the plasma arc torch200 can define, at least in part, liquid coolant channel 225A. In someembodiments liquid coolant channel 225A can be in fluid communication(e.g., connected via a fluid conduit, passage, tubes, etc.) with theliquid coolant channel 230. Liquid coolant channel 225A can be a supplyflow of liquid coolant. In some embodiments, liquid coolant channel 225B can be a return flow of liquid coolant. The gas flow channel 235 cansupply a shield gas to a workpiece.

In some embodiments, retaining cap 215 includes a shell (e.g., outercomponent 240) having an exterior surface (e.g., exterior surface 255)that defines, at least in part, liquid coolant channel 225A. Theretaining cap 215 can include a liner (e.g., an inner component 245)that is circumferentially disposed within the shell. The liner caninclude an interior surface (e.g., interior surface 265 of the innercomponent) that defines, at least in part, liquid coolant channel 230.Retaining cap 215 can include a gas flow channel 235 that is defined atleast in part by and located between the shell and the liner.

A shield retaining cap 220 can include an outer component 280 and aninner component 285. The outer component 280 of the shield retaining cap220 can include an interior surface 290 and an exterior surface 295. Theinner component 285 can be circumferentially disposed within the outercomponent 280. The inner component 285 can have an interior surface 300and an exterior surface 305. At least one of the inner component 285 orthe outer component 280 can be secured relative to a shield 205.

Liquid coolant channel 225A can be defined, at least in part, by aportion of the interior surface 300 of the inner component 285 of theshield retaining cap 220. In some embodiments, the interior surface 300of the inner component 285 and a retaining cap 215 (e.g., inner/nozzleretaining cap) define, at least in part, liquid coolant channel 225A.Liquid coolant channel 225B can be defined, at least in part, by theexterior surface 305 of the inner component 285 and the interior surface290 of the outer component 280 of the shield retaining cap 220. In someembodiments, liquid coolant channel 225A and 225B make up a firstportion of a liquid coolant channel and a second portion of the samechannel, respectively. In some embodiments the liquid coolant channels225A and 225B direct a coolant on to a shield 205. Liquid coolantchannel 225A can serve as a path for a coolant supply flow and liquidcoolant channel 225B can serve as a path to direct a coolant returnflow. The shield retaining cap 220 can also include a port 310 at an endof liquid coolant channel 225A and/or 225B. Port 310 can be disposedbetween the exterior surface 305 of the inner component 285 and theinner surface 290 of the outer component 280 of the shield retaining cap220. The port 310 can be disposed at an end of at least one of the outercomponent 280 or the inner component 285 of the shield retaining cap220.

In some embodiments, the shield retaining cap 220 can include a shell(e.g., outer component 280 of the shield retaining cap 220) and a liner(e.g., inner component 285 of the shield retaining cap 220). The linerof the shield retaining cap 220 can be disposed circumferentially withinan interior surface of the shell (e.g., interior surface 300 of theinner component 285 of the shield retaining cap 220). Liquid coolantchannel 225A can be defined, at least in part, by an interior surface ofthe liner. Liquid coolant channel 225B can be defined, at least in part,by a portion of the interior surface of the shell and a portion of anexterior surface of the liner (e.g., exterior surface 305 of innercomponent 285 of the shield retaining cap 220).

A method for cooling a plasma arc torch can include directing a liquidcoolant to an electrode (e.g., electrode 85 of FIG. 4), directing theliquid coolant to a nozzle 210 through a first liquid coolant channel(e.g., liquid coolant channel 230) defined, at least in part, by a firstretaining cap (e.g., retaining cap 215) and directing the liquid coolantfrom the nozzle 210 to a shield 205 through a second liquid coolantchannel (e.g., liquid coolant channel 225A and/or 225B) defined, atleast in part, by a second retaining cap (e.g., shield retaining cap220). Alternatively, in some embodiments, the sequence in which thecoolant is directed to the electrode, nozzle, and shield can be reversedor reordered.

FIG. 9 is a cutaway drawing of consumables of a plasma arc torch 315according to an illustrative embodiment. The plasma arc torch caninclude a retaining cap 215 and shield retaining cap 220 which candefine coolant channels 225A, 225B and a gas flow channel 235.

Retaining cap 215 can include an outer component 240 and inner component245. The inner component 245 of the retaining cap 215 can include aninterior surface 265 and an exterior surface 260. The outer component240 of the retaining cap 215 can include an inner surface 250 and anouter surface 255. The interior surface 265 of the inner component 245can define a portion of liquid coolant channel (e.g., liquid coolantchannel 230 in FIG. 8 above). Gas flow channel 235 can be disposedbetween or defined by the outer component 240 and inner component 245 ofthe retaining cap 215.

Shield retaining cap 220 can also include an outer component 280 andinner component 285. The outer component 280 of the shield retaining cap220 can include an exterior surface 295 and an interior surface 290. Theinner component 285 of the shield retaining cap 220 can include canexterior surface 305 and an interior surface 300. A liquid coolantchannel comprised of liquid coolant channels 225A and 225B can be formedby the outer component 280 and inner component 285 of the shieldretaining cap 220. Liquid coolant channel 225A can be formed at least inpart by the inner component 285 of the shield retaining cap 220 and anouter component 240 of a nozzle retaining cap (e.g., retaining cap 215).Liquid coolant channel 225B can be disposed between and defined by theouter component 280 and inner component 285 of the shield retaining cap220.

The shield retaining cap 220 can include a substantially cylindricalbody (e.g., body comprised of outer component 280 and inner component285) dimensioned to receive a shield 205 of the plasma arc torch. Theshield retaining cap 220 can include a liquid coolant channel (e.g.,comprising liquid coolant channels 225A and 225B) defined by thesubstantially cylindrical body. In some embodiments, liquid coolant issupplied via liquid coolant channel 225A, impinges a portion of theshield 205 (e.g., flange of the shield) and returns via liquid coolantchannel 225B. The liquid coolant channel can include a return path(e.g., liquid coolant channel 225B) and a supply path (e.g., liquidcoolant channel 225A) which directs a coolant to impinge acircumferentially extending portion 320 of the shield. The temperatureof the coolant impinging the shield 205 can be consistent at each pointalong the circumferentially extending portion of the shield 320.

In some embodiments, the substantially cylindrical body includes asubstantially cylindrical outer component (e.g., outer component 280)and a substantially cylindrical inner component (e.g., inner component285) disposed within the outer component. The supply path of the liquidcoolant channel (e.g., liquid coolant channel 225A) can be formed atleast in part by an interior surface (e.g., interior surface 300) of thesubstantially cylindrical inner component. In some embodiments, thereturn path (e.g., liquid coolant channel 225B) of the liquid coolantchannel is formed at least in part by an exterior surface (e.g, exteriorsurface 305 of the inner component) of the substantially cylindricalinner component and an interior surface (e.g., interior surface 290 ofthe outer component) of the substantially cylindrical outer component.

While the invention has been particularly shown and described withreference to specific illustrative embodiments, it should be understoodthat various changes in form and detail may be made without departingfrom the spirit and scope of the invention.

1. A retaining cap for a plasma arc torch comprising: an outer componenthaving an interior surface and an exterior surface which defines, atleast in part, a first liquid coolant channel; an inner componentcircumferentially disposed within the outer component and having anexterior surface and an interior surface which defines, at least inpart, a second liquid coolant channel; a gas flow channel defined atleast in part by the interior surface of the outer component and theexterior surface of the inner component; and a port located at an end ofthe gas flow channel between the interior surface of the outer componentand the exterior surface of the inner component.
 2. The retaining cap ofclaim 1 wherein the first liquid coolant channel is in fluidcommunication with the second liquid coolant channel.
 3. The retainingcap of claim 1 wherein the first liquid coolant channel is a return flowof liquid coolant.
 4. The retaining cap of claim 1 wherein the secondliquid coolant channel is a supply flow of liquid coolant.
 5. Theretaining cap of claim 1 wherein the gas flow channel supplies a shieldgas to a workpiece.
 6. The retaining cap of claim 1 wherein the interiorsurface of the inner component comprises a sealing assembly that sealsliquid coolant relative to a plasma arc torch body.
 7. The retaining capof claim 1 wherein the interior surface of the inner component issecured relative to a nozzle of the plasma arc torch.
 8. The retainingcap of claim 1 wherein the interior surface of the inner component and aplasma arc torch body define, at least in part, the second liquidcoolant channel.
 9. The retaining cap of claim 1 wherein the exteriorsurface of the outer component and an outer retaining cap of the plasmaarc torch define, at least in part, the first liquid coolant channel.10. A shield retaining cap for retaining a shield to a plasma arc torchcomprising: an outer component having an interior surface and anexterior surface; an inner component circumferentially disposed withinthe outer component and having an interior surface and exterior surface;and a liquid coolant channel comprising: a first portion of the liquidcoolant channel defined, at least in part, by a portion of the interiorsurface of the inner component; a second portion of the liquid coolantchannel defined, at least in part, by the exterior surface of the innercomponent and the interior surface of the outer component; and a portbetween the exterior surface of the inner component and the interiorsurface of the outer component and disposed at an end of at least one ofthe outer component or the inner component.
 11. The shield retaining capof claim 10 wherein the port is disposed at an end of the liquid coolantchannel.
 12. The shield retaining cap of claim 10 wherein the liquidcoolant channel directs a coolant on to a shield.
 13. The shieldretaining cap of claim 10 wherein the first portion of the liquidcoolant channel is a coolant supply flow.
 14. The shield retaining capof claim 10 wherein the second portion of the liquid coolant channel isa coolant return flow.
 15. The shield retaining cap of claim 10 whereinat least one of the inner component or the outer component is securedrelative to a shield.
 16. The shield retaining cap of claim 10 whereinthe interior surface of the inner component and an inner retaining capdefine at least in part, the first portion of the liquid coolantchannel.
 17. A retaining cap for a plasma arc torch comprising: a shellhaving an exterior surface that defines, at least in part, a firstliquid coolant channel; a liner circumferentially disposed within theshell and having an interior surface that defines, at least in part, asecond liquid coolant channel; and a gas flow channel defined at leastin part by and located between the shell and the liner.
 18. A shieldretaining cap for a plasma arc torch comprising: a shell; a linerdisposed circumferentially within an interior surface of the shell; anda liquid coolant channel comprising: a first portion of the liquidcoolant channel defined, at least in part, by an interior surface of theliner; and a second portion of the liquid coolant channel defined, atleast in part, by a portion of the interior surface of the shell and, atleast in part, by a portion of an exterior surface of the liner.
 19. Amethod for cooling a plasma arc torch comprising: directing a liquidcoolant to an electrode; directing the liquid coolant to a nozzlethrough a first liquid coolant channel defined, at least in part, by afirst retaining cap; and directing the liquid coolant from the nozzle toa shield through a second liquid coolant channel defined, at least inpart, by a second retaining cap.
 20. A plasma arc torch systemcomprising: a torch body including a plasma gas flow path for directinga plasma gas to a plasma chamber in which a plasma arc is formed; anelectrode; a nozzle disposed relative to the electrode to define theplasma chamber; and the retaining cap of claim 1, secured relative tothe nozzle.
 21. The plasma arc torch system of claim 20 furthercomprising a shield disposed relative to the nozzle and the shieldretaining cap of claim 10 secured relative to the shield.
 22. A shieldretaining cap for a plasma arc torch comprising: a substantiallycylindrical body dimensioned to receive a shield of the plasma arctorch; a liquid coolant channel defined by the substantially cylindricalbody wherein the liquid coolant channel comprises a return path and asupply path which directs a coolant to impinge a circumferentiallyextending portion of the shield.
 23. The shield retaining cap of claim22 wherein the temperature of the coolant impinging the shield isconsistent at each point along the circumferentially extending portionof the shield.
 24. The shield retaining cap of claim 22 wherein thesubstantially cylindrical body comprises a substantially cylindricalouter component and a substantially cylindrical inner component disposedwithin the outer component wherein the supply path of the liquid coolantchannel is formed at least in part by an interior surface of thesubstantially cylindrical inner component and wherein the return path ofthe liquid coolant channel is formed at least in part by an exteriorsurface of the substantially cylindrical inner component and an interiorsurface of the substantially cylindrical outer component.